SCREW COMPRESSOR

A screw compressor according to some embodiments includes a screw rotor, a rotor casing accommodating the screw rotor, and an internal-volume-ratio-adjusting valve capable of changing internal volume ratio. The internal-volume-ratio-adjusting valve includes a valve body movable along an axial direction of the screw rotor and defining a gas-discharge position, and a cylinder containing at least one pressurizing chamber with a cylinder rod and a piston. The cylinder rod is coupled to the valve body and disposed along the axial direction. The piston is fixed inside the pressurizing chamber to the cylinder rod and divides the pressurizing chamber into two pressurizing spaces along the axial direction. The screw compressor further includes a first communication passage connecting one of the two pressurizing spaces with the discharge gas passage, and a second communication passage connecting the other with a just-before-discharge tooth space immediately before a tooth space that communicates with the discharge port.